The hydration oftricalcium silicate was followed at a water/C:,S ratio of 0.7 between 5' and 5O'C by determining free lime and combined water. Free lime was estimated by the o-cresol method, whereas combined water was calculated from the amount of free water remaining in the paste as determined by extraction with methyl ethyl ketone. The ratio of free lime to combined water was constant throughout the hydration: this ratio indicated that CSH(II) may be represented as 1.68Ca0 . SiO, . 2.58Hp0. When maximum supersaturation of the solution with Cap+ is attained, the induction period terminates and the reaction proceeds rapidly, probably as the result of propagative surface nucleation-growth of CSH(I1). Kinetic equations were derived for these reactions. When the surface of C:,S is entirely covered by CSH(II), the reaction becomes slow and is controlled by diffusion of water. Constants involved in the kinetic equations are evaluated and discussed.

Calcium silicate hydrates (C-S-H), prepared a t 20 "C and 50 "C to have various CaO : SiO, molar ratios ( n ) , were examined for their compositions with particular attention to the combined water contents and to their solubilities in water a t 30 "C. The C-S-H gels may be described as solid solutions of the type nCaO.SiO,.( n + 0.8) H,O, where n 2 0.8. A thermodynamic treatment was developed which enabled n to be calculated from solubility data; the n values observed were compared with those calculated. The conclusion reached was that non-equilibrium was liable to occur owing to the immature state of C--S-H. Also observed was the unusual property that the response to the varying calcium ion concentrations in the solutions was limited to within the surface layer of the C-S-H particles. The possible phase relations under the state of equilibrium are presented.KNOWLETIGE of the coniposition and properties of calcium silicate hydrate, KaO.SiO,(aq) (hereafter abbreviated as C-S-IT) ,t ancl its equilibrium is very irnportant in

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The decomposition of hydrogen iodide serves as the hydrogen-evolution step in several thermochemical water-splitting cycles, including the Magnesium–Iodine cycle. A kinetic analysis of the catalytic decomposition of hydrogen iodide has been carried out by the use of a flow method at 500–700 K. The platinum-supported active carbon catalyst (1 wt%) and the active carbon catalyst which have been found effective in the research reported previously, are used as the catalysts. The contact time-conversion relationships for both the catalysts are simulated successfully on the basis of an assumed reaction scheme. The influence of water vapor on the rate and the equilibrium of the decomposition of hydrogen iodide is negligibly small. The inhibition effect of iodine on the rate of the decomposition of hydrogen iodide over the platinum-supported active carbon catalyst is remarkable below 550 K.

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